The present invention relates to vehicle seats in which the height of the seat proper is adjustable.
More particularly, amongst such vehicle seats, the invention relates to those comprising a vehicle seat comprising a back and a seat proper which extends in a longitudinal direction between a rear end close to the back and a front end remote from the back, said seat proper comprising a rigid frame supported by a raising mechanism for moving the seat proper upwards or downwards. Such seats are known in particular from U.S. Pat. No. 4,782,715. The raising mechanism is controlled by an actuator comprising a tube having a nut fixed at one end thereof and having a screw rotated by a motor and co-operating with the nut, the screw of the actuator being provided with a free end situated inside the tube of the actuator, the raising mechanism further comprising an elastically-deformable member for assisting the motor of the actuator while moving the rigid frame upwards.
In that known type of vehicle seat, the elastically-deformable member is generally constituted by a helical spring which exerts a traction force on certain portions of the raising mechanism, in particular on pivots, in order to urge the seat proper, or more precisely the rigid frame of the seat proper, upwards. The helical spring which is placed at a distance from the actuator thus serves to assist the actuator while moving the rigid frame upwards.
Nevertheless, since the helical traction spring is dimensioned to compensate substantially for the average weight of a user sitting on the seat, it will be understood that the spring thus generates large forces within the raising mechanism. Given the fact that the spring is generally located close to one side of the seat proper and that the actuator is generally located close to the other side thereof, these large forces give rise to deformation of the frame of the seat proper, thus causing friction in the pivots and consequently losses in the efficiency of the motor-driven actuator.
Similarly, the dimensions of the spring make it complicated to mount on the raising mechanism and the bulk of said spring makes it necessary to place the actuator at a distance therefrom, thus making it impossible to adjust accurately the clearance which exists between the screw of the actuator and the nut secured to the tube.
Finally, the traction spring can also be caused to vibrate, in particular when the vehicle is running or because of vibration from the engine, with the traction spring then transmitting the vibration to the moving part of the raising mechanism and thus to the entire rigid frame of the seat.
An object of the invention is to remedy the above-mentioned problems.
The invention achevies this object by the facts that the elastically-deformable member is housed inside the tube of the actuator between the free end of the screw of the actuator and a support element secured to the tube of the actuator.
Thus, the elastically-deformable member is directly integrated in the actuator so that the forces it exerts are no longer located on the moving part of the raising mechanism, but inside the actuator, thus making it possible advantageously to eliminate all axial play between the nut and the screw of the actuator and vibration phenomena on the raising mechanism. Furthermore, integrating the elastically-deformable member in the actuator makes it possible to provide a single module that is compact can that can be mounted directly on the raising mechanism so as to assist the motor of the actuator while it is moving the rigid frame of the seat upwards.
In preferred embodiments of the invention, use can also be made of one or more of the following dispositions:
the elastically-deformable member operates in compression to urge the free end of the screw away from the support element;
the raising mechanism comprises at least four links distributed as a pair of front links and a pair of rear links, which links pivot in vertical planes parallel to the longitudinal direction when the raising mechanism is in operation, the two links of each pair of links being supported respectively by bottom pivots sharing common pivot axes, the bottom pivots being connected to supports for connecting to the floor of the vehicle, and these two links being connected respectively to the rigid frame via top pivots which likewise share common pivot axes, said actuator having a first end connected to one of the links of the raising mechanism and a second end connected to the support;
the actuator is designed to work in retraction during upward displacement of the rigid frame, and the support element is constituted by the nut of the actuator tube, the elastically-deformable member being disposed in an annular housing defined by the screw of the actuator and the tube of the actuator, and said elastically-deformable member being compressed between the nut of the tube and the free end of the screw of the actuator;
the actuator is provided with an abutment member for limiting the stroke of the actuator screw during downward displacement of the rigid frame;
the abutment member is constituted by a tubular member placed in the annular housing and surrounding a portion of the actuator screw, the tubular member having a first end connected to the nut of the tube and a second end for coming into contact with the free end of the actuator screw;
the actuator is designed to operate in extension during upward movement of the rigid frame, and the support element is constituted by an end wall of the tube co-operating with the free end of the actuator screw to define a cylindrical housing in which the elastically-deformable member is disposed;
the free end of the actuator screw includes an abutment member for coming into abutment against the nut of the actuator tube;
the elastically-deformable member is constituted by a compression spring; and
an additional compression spring is placed in the cylindrical housing concentrically with the first compression spring.